Inductors are used in a wide variety of applications. This application describes an inductor that is particularly suitable for high power, high frequency applications, such as in a high frequency DC-DC switched mode power converter. An inductor assembly according to the present invention is also useful in other applications, such as transformers.
An example of a complex DC-DC power converter is described in WO 02/101909. FIG. 1 is a generalised circuit diagram of the most basic elements of a DC-DC power converter, as described in WO 02/101909. This power converter is suitable for use in high power applications, such as power conversion in electric vehicles. In use, the switches S1 and S2 are never both closed but are driven so that one is open while the other is closed, using a pulse width modulation (PMW) drive signal, with a variable mark-space ratio. It can be seen that, to first order, when S2 is closed, current through the inductor L increases linearly and when S1 is closed it decreases linearly, so that the current waveform has an asymmetric sawtooth profile, with a DC component. The voltage ratio between input and output is simply determined by the ratio of the time S2 is switched on to the total cycle time. This sawtooth current signal is then filtered by the passive circuit formed by the inductor L and the capacitor C2, which is operating as a low pass filter at a frequency well above resonance to give a voltage ripple at the output terminal B which is acceptably low. It is advantageous that switching is at the highest practical frequency, in order to minimise the size and cost of the filtering components L and C2.
The inductor L in FIG. 1 therefore has to operate at high frequency (e.g. 100 kHz) and at high power (1 kW to 10 kW). The inductor should, ideally, introduce minimal loss into the system and be of low volume, low mass and low cost.